__________________modverb, transitive /mod/ to state that one is utterly clueless about the operation of device to be "modded" and into "fixing" things that are not broken; "My new amplifier sounds great so I want to mod it."

Well, the "mosfets" look exactly like the KSA940, a PNP transistor. I wonder why they would use an all PNP output stage. Looks like a design from the late 1950's. Also there is no temperature compensation at all, so it is possible that these amps self-destruct by thermal runaway.
I'll probably scrap the Amp PCB. It's no good at all.

I can't imagine how a mosfet amp without manual bias adjustment should work in any reasonable way. VGS is usually all over the map. Matching is too expensive for cheap amps, anyway. VBE of bipolars is perfect in comparison.

Hmm - where does the bases/gates (most left pin) of the lower and the upper outputs go exactly? ( you have drawn them differently in your schematics so it is hard to gues) Double check that so that we can conclude what type it is.

Hereafter 2 options:
1) Replace all outputs with cheap new ones, and add a proper bias circuit.
2) Replace the PCB with DXamp or Symasym, and mount a decent heatsink.

Also there is no temperature compensation at all, so it is possible that these amps self-destruct by thermal runaway.
I'll probably scrap the Amp PCB. It's no good at all.

Hm, that D2, 1N4148 should be mounted or at least touching the heatsink to ensure some thermal tracking. Anyways, like you said, that piece of junk isn't worth repairing. Replace it with some reliable design.

Hm, that D2, 1N4148 should be mounted or at least touching the heatsink to ensure some thermal tracking. Anyways, like you said, that piece of junk isn't worth repairing. Replace it with some reliable design.

I just noticed the value of R7 - 33ohms - this is a pure class B design!

Svokke : If you want good sound you should skip the original pcb, and put in another amplifier.

almost the same amp design can be found in those "hollywood" or "skytec" or "nightline" or whatever amps you can get off ebay here in germany. they are also rated 480 watts (although there is an even cheaper model rated 240 watts, which has only two output transistors per channel)... i have the schematic diagram of these amps somewhere, perhaps i'll find it, so i can upload it here.